Convert merged module lib stub to api.go

Bug: 169103987
Test: m framework-updatable-stubs-module_libs_api and diff intermediates
      folder before and after.
Change-Id: I6018791ae136bc764a6e846078c6bce59bcc123b
diff --git a/api/Android.bp b/api/Android.bp
index 7aa68f8..362f39f 100644
--- a/api/Android.bp
+++ b/api/Android.bp
@@ -32,6 +32,7 @@
         "soong",
         "soong-android",
         "soong-genrule",
+        "soong-java",
     ],
     srcs: ["api.go"],
     pluginFor: ["soong_build"],